Although I think we have strayed from the OP, I will add my two cents. I have learned in other aspects of competition, that the very fine details and differences that affect performance for the better or worse are only noticed by the more experienced individuals. I am an amateur when it comes to guns, and porting may not affect my performance at all, but when you get to higher levels of competition, EVERYTHING affects performance. I may not even be able to tell a 20 guage from a 12, if blind folded. I bet a professional could(or even experienced amateurs). If you change anything with the gun, drill holes in the barrel for instance, things change.
Amateurs practice until they get it right. Professionals practice until they don't get it wrong.